Engine fuel additives



United States Patent m 3,397,969 ENGINE FUEL ADDITIVES James W. Tooke, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Apr. 25, 1966, Ser. No. 544,697 7 Claims. (Cl. 44-57) ABSTRACT OF THE DISCLOSURE Addition of hexaalkylditin compounds to hydrocarbon fuels improves the combustion chartacteristics of such fuels.

This invention relates to combustion modifiers for fuels and to a method for improving the combustion of such fuels. In one aspect, there is provided an engine fuel composition comprising a combustible hydrocarbon or derivative thereof and a small amount of a hexaalkylditin compound. In another aspect, a combustion modifying amount of a hexaalkylditin compound is added to a hydrocarbon engine fuel to improve the combustion characteristics thereof. In yet another aspect, a hexaalkylditin compound, wherein the alkyl radical has from 1 to about carbon atoms, is added to a hydrocarbon engine fuel in a relatively small amount sufiicient to improve the octane rating of the hydrocarbon fuel. In yet another aspect, the performance of hydrocarbon engine fuels is substantially improved by effecting the ignition and combustion of said hydrocarbon fuels in the presence of a combustion modifying amount of a hexaalkylditin compound.

Hydrocarbon fuels intended for application in relatively high compression internal combustion engines can be manufactured and refined to such an extent that they are of sufficient quality to provide the desired combustion characteristics without the necessity of effecting such combustion in the presence of modifying agents. However, the refining techniques required to produce fuels of such high quality, of course, add appreciably to the cost of the fuel. In addition, the demand for even higher quality in such fuels is continually increasing and becoming even more critical with the introduction of higher compression engines. As a result, it has been a practice for some time to combine combustion improving additives with these hydrocarbon fuels to achieve the desired combustion characteristics without the necessity of producing a hydrocarbon mixture that will itself provide the desired results. These additives have met with varying degrees of commercial success due primarily to the differences in expense, performance characteristics and combustion product contaminant level. In particular, when hydrocarbon fuels containing lead and anti-knock or .octane improving agents are burned in internal combustion engines, at least a portion of the additive is converted to a deposit of non-volatile lead compounds which accumulate on the various parts of the engine which result is, .of course, very undesirable. In addition, the additive combustion products that migrate from the engine and exhaust system are also non-volatile and, as a result, become dispersed in the atmosphere in the form of fine smoke particles, thereby resulting in contamination of the atmosphere. We have found that through the use of the hydrocarbon fuel additive of this invention the desirable improvement in combustion characteristics can be achieved while substantially reducing the detrimental characteristics of the combustion products.

It is therefore an object of this invention to provide a novel fuel composition having improved combustion and octane properties. It is another object of this invention to provide a novel gasoline range hydrocarbon fuel composition for internal combustion engines. It is yet another object of this invention to provide a hydrocarbon engine fuel 3,397,969 Patented Aug. 20, 1968 composition having therein a novel hydrocarbon fuel additive, which fuel composition has improved combustion characteristics and which produces combustion products of substantially reduced detrimental contaminant level.

Other aspects, objects and the several advantages of this invention are apparent to one skilled in the art from a study of this disclosure, and the appended claims.

In accordance with this invention, the efiiciency and quality of combustion of hydrocarbons is greatly improved by effecting the combustion of the hydrocarbons in the presence of a relatively small amount of a hexaalkylditin compound, sufiicient to improve the octane rating of the base fuel. For application with conventional hydrocarbon fuels designed for use in internal combustion engines the alkyl constituents of the ditin compounds preferably have from 1 to about 5 carbon atoms. It is not necessary that all of the alkyl constituents in any given additive molecule have the same number of carbon atoms. On the contrary, each molecule can contain alkyl substituents of several different species.

The hexaalkylditin compounds of this invention are suitable additives for essentially all combustible hydrocarbons in addition to oxygenated derivatives thereof. However, they are most advantageously employed to improve the combustion efiiciency of internal combustion engine fuels and particularly gasoline range hydrocarbons. Such fuels generally include gasolines, benzene, fuel oils, kerosene, alcohols, or blends or mixtures thereof. The improvement in combustion eiiiciency that results through the use of the composition of this invention is manifested by an improved antiknock performance of the engine, by increased mileage obtained from the base fuel in a given engine, by the permissible use of leaner fuel-air mixtures, and by increased power output.

The hexaalkylditin compounds of this invention are sufficiently volatile within the range of operating temperatures realized in conventional internal combustion engines to allow their volatilization along with the hydrocarbon base fuel prior to combustion. The additives of this invention further have the advantage of having very low volatility at ambient conditions which provides the advantage of easier storage, handling and formulation.

The improved fuel composition of this invention generally comprises a relatively small amount of the hexaalkylditin additive sufficient to achieve the desired improvement in octane and anti-knock properties. These amounts are, of course, generally so small that the additives do not themselves substantially augment the theoretical combustion energy of the base hydrocarbon fuel. In the presently preferred embodiment of this invention, the hexaalkylditin compounds can be dissolved in a gasoline range hydrocarbon fuel. The boiling points of such fuels are generally within the range of from about to about 450 F. in amounts of up to about millimoles per gallon of hydrocarbon base fuel. Under such conditions, the octane of the hydrocarbon base fuel can be increased by as much as 7 percent. I have also found that although the higher homologs of the ditin fuel additives are effective in improving the quality of the final composition, it is generally preferable to employ the lower molecular weight homologs such as for example hexamethylditin, hexaethyl ditin, hexapropylditin, hexaamylditin, and hexabutylditin as additives, as well as hexaalkylditin compounds comprising dissimilar alkyl constituents such as dimethyltetraethylditin, tetramethyldibutylditin, triethyltriamylditin, and trimethyltributylditin.

The following examples illustrate the improvement that can be achieved through the use of the additives of this invention.

A primary fuel mixture consisting of 80 volume percent isooctane and 20 volume percent normal-heptane was used 3 as test fuel in the standard knock test procedure. (ASTM D 357-65).

Reasonable modification and variation of the concept of this invention will be apparent to one skilled in the art in view of the foregoing disclosure and the appended claims to this invention, the essence of which is that there is provided an improved hydrocarbon engine fuel composition comprising a small amount of a hexaalkylditin combustion modifier.

I claim:

1. An engine fuel composition comprising primarily combustible hydrocarbon and having therein an amount of a hexaalkylditin compound of sufiicient volatility to vaporize at operating conditions, said amount being sufficient to improve the ignition and combustion of said hydrocarbon.

2. The composition of claim 1 wherein the alkyl of said hexaalkylditin compound has from 1 to about 5 carbon atoms.

3. The composition of claim 1 wherein said compound t is selected from-the group consisting of hexamethylditin and hexabutylditin.

4. The composition of claim 1 wherein said hydrocarbon comprises primarily gasoline range hydrocarbons.

5. The composition .of claim 2 wherein said amount is up to about millimoles per gallon of said hydrocarbon and wherein said hydrocarbon comprises primarily gasoline range hydrocarbons.

6. A method for improving the performance of hydrocarbon engine fuels, which method comprises effecting the ignition and combustion of said hydrocarbon in the presence of a combustion modifying amount of a hexaalkylditin compound wherein the alkyl radical has from 1 to about 5 carbon atoms.

7. A method of claim 6 wherein said hydrocarbon comprises primarily gasoline range hydrocarbons, said hexaalkylditin compound is selected from the group consisting of hexamethylditin and hexabutylditin and said combustion modifying amount is within the range of up to about 100 millimoles per gallon of said hydrocarbon.

R. K. Ingham et al., Organotin Compounds, in Chemical Reviews, vol. 60, No. 5, pp. 514-516, October 1960.

DANIEL E. WYMAN, Primary Examiner.

W. J. SHINE, Assistant Examiner. 

